A series of studies which examine the effect of antibody and complement on the immune clearance of erythrocytes was continued. Erythrocytes coated with IgM antibody are cleared by a complement dependent mechanism by the RES of the liver and then are released back into the circulation as Coombs positive cells. Studies with cold agglutinins demonstrated that this above-noted effect is independent of antibody and only depends on the interaction of complement fragments with cells of the RES. Also, the sites of C3 deposition were shown to differ for anti I cold agglutinins and other IgM anti RBC antibody and were found to operate essentially independently of one another.